My Viessman boiler journey

[marshian]

Background

Current house owned 33 years but updated over the years early 1980's built detached 4 bed so originally

1.      Open cavity walls.

2.      25mm of loose fill loft insulation.

3.      Single glazed doors and windows.

4.      Suspended floor downstairs over a 2 - 3 ft crawl space.

5.      Heat only boiler (non condensing).

6.      T11 rads in some cases sized a little on the mean side.

Back in 1991 we had an annual gas usage for CH and HW of 25,000 kWh

It’s two floors with a total floor area of 113 m2 (Small extension done in 2006 to building regs at the time) have reduced energy consumption over the years with Double Gazing, Cavity wall insulation, upgraded loft insulation (75mm so could still be better), new condensing boiler got us down to 16,500 kWh per year

Most recently every rad in the house has been replaced basically changing T11’s for T22’s of similar or larger size and a few verticals where space for T22’s was a challenge or SWIMBO demanded something “more modern”

I also spent 3 months in 2022 doing 56m2 of 75mm PIR between the joists under the ground floor. The PIR was an amazing reduction to heat loss considering heat is supposed to rise but the airflow under the house is quite a high rate when the wind blows with one air brick every five bricks outside (house was built near a flood plain and the water table is quite high)

The other contributor may or may not be fitting Wiser controls and Smart TRV's but last winter I ran it like an on/off timer rather than a 24/7 with setbacks due to issues I had with heating controls (old sunvic wiring centre with relays)

I was running a manual weather compensation for CH and turning the flow temp up to do HW 

The last few improvements got us down to 8500 kWh gas usage per year for CH and HW but the current boiler for last 14 years was driving me nuts. It was a Glow Worm Flexicom 24HX (So 10 kW min) and it cycles like crazy. When I did the heat loss calcs it confirmed to me that we had a heat loss of 4,500 kWh at -2 so clearly there was a good reason why it cycles.

Annoyingly I replaced the vented HW tank a few years ago (old one needed 1 hr to heat water due to scale inside - hard water area) so it's not that old but I'm sure you are right if I could get a better vented HW tank with a high surface area coil it would probably help a lot when at lower flow temps (at the same time I fitted a water softener so I'm not expecting the same level of scale build up impacting water heating performance)

So with the boiler driving me crazy and wanting to bring forward potential big spends to before I pack up work I wanted to buy the right boiler this time.

So I did a lot of looking at boilers before deciding on a Viessmann 100W “Heat Only”

I wrote a short brief of the “Proposed System”

Boiler Required: Viessmann Vitodens 100-W B1GA 16 kW

Location same place as existing Glow-Worm Flexicom 24HX

Flue needs to be supplied and fitted with a plume management kit (vertical after exit thro wall as a car port is next project)

External wired weather compensation sensor

Wifi Link Board (So I can link to Home Assistant).

Convert to DHWP with CH being the rest position (normally open) on a 3 port (2 position valve) or two zone valves NO for CH and NC for HW

Set up to weather comp for CH flow temps (38 to 50 so slope of 1.4 as a start point but I think it will end up at 1.2) and full boiler output at 80 for HW requirements

Considering HW cyl replacement with larger coil for lower flow temp water heating but may do this at a later stage as the efficiency gains from heating HW at lower flow temps in summer are quite small.

I asked a few local gas engineers to quote but most either weren’t Viessmann trained (so no chance of the 10 year warranty) or wanted me to accept a different boiler (WTF is that all about)

Anyway one gas engineer was Viessmann trained and said he could do what I wanted and came back with a quote of £3600....... (ouch)

I gave it some thought........

A lot of thought.......  £3600 buys a lot of gas!!!!! (About 72,000 kWh at current prices so I could cover the heating needs of my house for 8.5 years.........)

[JohnMo]

Also try Atag boilers, they are super quiet, they also start up at min modulation and slowly ramp up. Most boilers work the other way around.

 

16kW sounds big for your heat losses, you need to get one with good modulation and sized to suit heat loss.

 

You seem to have zoned the house a lot, you need to be careful you aren't cycling the boiler too much for good gas consumption. The lower the flow temperature the less the boiler can modulate down.

 

Most plumbers know S and Y plan and are then out of their depth. Look for a plumber that understands heat pumps and then the install should be quite straightforward.

 

The other option for boilers, is you find one at a good price, get the plumber to install per your instructions and take a risk on warranty. Pretty much what I did. Or you can do most the courses yourself online via Viessmann if you want. Then you carry the warranty instead of the plumber.

 

 

 

 

[marshian]

2 minutes ago, JohnMo said:

Also try Atag boilers, they are super quiet, they also start up at min modulation and slowly ramp up. Most boilers work the other way around.

 

16kW sounds big for your heat losses, you need to get one with good modulation and sized to suit heat loss.

 

You seem to have zoned the house a lot, you need to be careful you aren't cycling the boiler too much for good gas consumption. The lower the flow temperature the less the boiler can modulate down.

 

Most plumbers know S and Y plan and are then out of their depth. Look for a plumber that understands heat pumps and then the install should be quite straightforward.

 

The other option for boilers, is you find one at a good price, get the plumber to install per your instructions and take a risk on warranty. Pretty much what I did. Or you can do most the courses yourself online via Viessmann if you want. Then you carry the warranty instead of the plumber.

 

 

 

 

 

I'm not going to reply to all your very good points in turn for a couple of rreasons

 

I'm kinda going back to April this year when I was decided on what I wanted and will move shortly to July when it was installed...............

 

It modulates down to 3.1 kWh and my intention is very much to "zone less" once the "issues" with the install are resolved....... This will be My Viessmann boiler journey "part II"

[Huckleberrys]

Speak to viessman, they will let you know trained installers in your area. I myself am a viessman installer and they are fantastic boilers and what you are suggesting is not a hard task for anyone really...was the £3600 including supply of all materials? 

 

On another note I would steer clear of atag, my experience in the past is of nothing but trouble with badly built boilers 

[marshian]

4 hours ago, Huckleberrys said:

Speak to viessman, they will let you know trained installers in your area. I myself am a viessman installer and they are fantastic boilers and what you are suggesting is not a hard task for anyone really...was the £3600 including supply of all materials?

 

I did and apart from the engineer I used the nearest alternative Viessmann installer was 55 miles away and he wasn't interested in travelling for the job and as a result quoting for it either...... Problem with living in East Anglia I guess.

 

The £3600 was including all materials on the quote below

 

Drain down current heating system and remove boiler from kitchen

 

Supply and install a Viessmann 100w 16kw heat only boiler

 

Supply and install a weather compensation sensor on north facing wall

 

Supply and install the WI-FI module to boiler

 

Supply and install a new flue with plume management kit

 

Connect gas pipe and adjust as needed

 

Connect condensate and adjust a needed

 

Convert the heating and hot water system to a S plan with a normally open zone valve and a normally closed zone valve giving hot water priority

 

Commission boiler

 

Register with Viessmann for a 10 year warranty

 

Register with Gas Safe

 

Five days prior to start date we would need to add a system cleaner to the current system so we can chemical flush it in the day of the
install

A 50% deposit is required before the start date with remainder on completion

 

That should have rung alarm bells with me

 

What I got was a weather compensated boiler in an std S plan set up with NC zone valves on both HW and CH

 

It also doesn't know if it's doing HW or CH so weather compensation is pretty bloody useless unless I want to heat water at 35 deg flow temp

 

I was just a little bit piddled off on the day when he finished the install and said so how do I set the temp for water to be different for CH and he said you just set the flow temp to 55 Deg..................

[marshian]

So to continue on a more positive note

 

After the boiler was fitted I explained to the gas engineer that I wasn't exactly a happy customer but as he had done everything he said in the quote I would settle the balance however I would like him to supply what I asked from an operating perspective

 

I sent him

 

1. links to various X-Plan set ups (Both web sites and youtube videos)

2. Details of Viessmann part number 7574319 cunningly titled "Cylinder demand terminal box"

3. Links to suppliers of NO zone valves

4. Kimbo write up of why DHWP should be used

 

I was being helpful although I would have expected someone who was asked for DHWP and specifically a combination of NC and NO zone valves to maybe say - actually fella you're speaking a different language to me - can you help me understand it.......

 

Anyway this Friday he's coming back with a NO Zone valve, Cyl demand box and the wifi module which has been on back order since the boiler was fitted and hopefully we can keep the smoke in the wires.

 

Because in my original brief I did put "The boiler change is not to save gas – it’s to stop me having to constantly manually adjust the flow temps based on expected weather and having to heat water at elevated flow temps manually. I’ve got other hobbies I’d rather concentrate on."

 

[marshian]

So Friday progress - some good, some not so good but might be normal - who knows???

 

System drained down (so we could swap out the zone valve)

 

HW demand box fitted and wired into the boiler - that required lifting some floors again as well as feeding it alongside the flow and return pipes from boiler to HW tank.

 

Wifi module fitted - getting that to work involved a bunch of calls to Viessmann technical help

 

NC Zone valve for CH swapped out for the NO zone valve

 

System refilled - christ I hate how bad this system is from a drain down - my last resort is often putting a hose on one of the drain points and sticking mains pressure up the pipe......

 

Massive air lock again - every bloody time this system is a cow to re-fill) eventually opening the lowest point drain valves for both flow and return as well as the boiler drain valve o they flowed resulted in a shit load of spluttering followed by a decent flow and then all the rads filled and bleed out nicely

 

Boiler then re-set up with weather compensation (wasn't done last time because I didn't want weather compensated HW heating) we set the slope to 1.4 (which is the default) I actually think 1.2 will work but lets be on the high side we can always decrease or increase if my guess is wrong............

 

So time to fire it up and that's where the fun started

 

Needed some HW for bath night

 

HW selected boiler fires up 60 deg flow temp set point - well that's a bit crap can we ramp it up a bit - bath night I normally run the boiler at 70 deg flow to get the tank to 60 deg.

 

No matter what we tried the 60 deg was the max............... so HW demand box ignores the weather comp but caps the flow temp to 60 deg C

 

45 mins later I had a tank of 50 deg water and I took the attitude that that'll bloody do if she wants a hot bath she'll have to drain the damn tank

 

Lets do CH

 

Boiler capped at 37 deg C - I can lower it but not increase it - it's maybe 12-13 outside so that kinda lines up with the slope (ish)

 

 

 

Lets give it a go

 

So what I expected - boiler would fire up drive up at a fairly soft rate initially - it would monitor the flow and return and with a stone cold system wind up the burner to match the flow and get up to target temp fairly quickly

 

It did just that but over shot 37 deg - that's OK I thought it often exceeds the flow temp by up to 6 deg to keep running rather than cycle (neat trick that unless you have flow and return temp monitoring you'd never bloody know but I have just that set up so no concerns here)

 

At an actual 56 deg flow temp I had concerns!!!!

 

I'll do what I did next in another post because I need some screenshots from my phone and they aren't on this PC so just imagine the Eastenders theme tune is banging away as this post ends

 

[marshian]

Ok so I downloaded the vicare app at this point I wasn’t looking for a solution I wanted to understand what was going on

 

 

So there you are the weather comp curve in the app

 

WTF is going on!!!!!

 

Lets see if I can change that

 

 

That’ll do for now

 

hit save and boiler does a massive stall and modulates down to 3/5th’s of (expletive deleted) all and temps start falling fast

 

It actually then cut out and 20 mins later fired up at a nice 37 deg C and 10.6 % modulation (which I cannot work out as kWh because it makes no sense at all)

[marshian]

And today I has nothing……,

 

CH - all rads call for heat, pump fires up and water circulating at 1.1 m3/hr - boiler does nothing

 

HW - (CH zone closes HW zone valve opens), tank stat is calling for heat, water is circulating at 1.2 m3/hr - boiler does nothing 

 

cool beans!!!!!

 

[JohnMo]

1 hour ago, marshian said:

CH - all rads call for heat, pump fires up and water circulating at 1.1 m3/hr - boiler does nothing

WC normally has the circulation pump pump running 24/7. Room stats are also either deleted or set a few degrees warmer than room target.

 

Maybe the circulation temp is above the set point controller hysterisis. That's the thing with WC, it's not always heating, mine spends most it's time just circulating. Add heat for 20 to 40 mins takes a few hrs off. As the day gets warmer the set point for the water lowers so the boiler or heat pump doesn't need to add heat.

 

If in doubt switch off for a few minutes and switch back on. Sometimes lots of setting changes just confuse the controller and it's needs a reset.

 

 

[MrPotts]

Are you now using manual TRV’s on your radiators or do you still have the Wiser kit installed?

[marshian]

11 minutes ago, MrPotts said:

Are you now using manual TRV’s on your radiators or do you still have the Wiser kit installed?

One manual on the bypass rad all the rest are wiser

[marshian]

2 hours ago, JohnMo said:

 

If in doubt switch off for a few minutes and switch back on. Sometimes lots of setting changes just confuse the controller and it's needs a reset.

 

 

Oh I tried the switch it off and on again trick…..

 

Boiler now reset to dumb boiler - no weather comp (well I’m doing manual weather comp based on what I think the house needs) and it’s heating water and running CH fine

 

Waiting on Viessmann technical before we try this WC and HW demand thing again 

 

Tomorrow the job will be running a cable from pump back to the boiler so boiler has control of the pump - should stop the 75 errors I’m getting when Wiser decides to pause the heating.

 

Floor is up in places already so might as well do that

 

Quite tempted to run another run of 22mm copper to split the flow and returns (currently they are slapped together in the same notched joist) then I can insulate the pipes individually 

 

we shall see how today goes (roofing the shed with EPDM has priority before the weather turns to shit)

 

 

 

 

[MrPotts]

1 hour ago, marshian said:

One manual on the bypass rad all the rest are wiser

I thought you still had the Wiser TRV's. I have been slowly removing my Wiser TRV's as I just couldn't have the Wiser system turning on the boiler for one radiator, what a waste of gas and boiler efficiency. Out of 13 radiators I now only have 3 Wiser TRV's, all the other radiators are using manual TRV's and the 3 bathroom radiators have no TRV's.  The Wiser TRV's I still have installed are 2 in the lounge (controlled by a Wiser room stat) and 1 in the hall.  This has resulted in more radiators heating up when the boiler fires and much better efficiency.

[marshian]

45 minutes ago, MrPotts said:

I thought you still had the Wiser TRV's. I have been slowly removing my Wiser TRV's as I just couldn't have the Wiser system turning on the boiler for one radiator, what a waste of gas and boiler efficiency. Out of 13 radiators I now only have 3 Wiser TRV's, all the other radiators are using manual TRV's and the 3 bathroom radiators have no TRV's.  The Wiser TRV's I still have installed are 2 in the lounge (controlled by a Wiser room stat) and 1 in the hall.  This has resulted in more radiators heating up when the boiler fires and much better efficiency.

I’ve set the TRV setback at night to 10 deg lower than day time setting to stop that issue happening at night - day time I’m hoping that weather comp and the correct flow rates thro each rad stops that happening.

 

Last year I stopped Wiser intervening on the approach to target room temps by having one TRV set to 5 deg higher than target room temp and not having it on the rad (std non smart TRV was on the rad) that and a pump overun stopped the Wiser from shutting down the heating and leaving the boiler hot and kettling

[marshian]

This is why I think I need to give the boiler control of the pump

 

 

It happens so frequently the last message from the vicare app was

 

 

That’s definately Wiser buggering around trying to save a bit of gas 

 

If I give the boiler control of the pump it won’t be able to stop it - as a result it’s regular attempts at saving gas will be thwarted 

I might have to go back and tell Wiser it’s an Oil Boiler not a gas boiler again - that helped a lot with the old boiler but I’d told it it was a gas boiler again when I had the new boiler installed (clean slate and all that)

 

[MrPotts]

You're using WC so why are you also using individual room stats (Wiser TRV's).  I think you would be better using manual TRV's and just limiting the temps for each room as required.  I think the Wiser system may be in conflict with the boiler and WC.

[JohnMo]

21 minutes ago, marshian said:

might have to go back and tell Wiser it’s an Oil Boiler not a gas boiler again

Or just delete them. Just run WC. Put normal TRVs in bedrooms. If you have radiators randomly switch on and off you just end up short cycling the boiler and undo any savings made.

[marshian]

Do people not read posts

 

WC is turned off because it’s not working

 

when it is I may well ditch Wiser altogether 😉

[JohnMo]

1 hour ago, marshian said:

Do people not read posts

 

WC is turned off because it’s not working

Was saying this instant, I was implying when it is working.

[marshian]

1 hour ago, JohnMo said:

Was saying this instant, I was implying when it is working.

And it is something I will seriously consider (save me a few quid in batteries every year and stops SWIMBO winding up the TRV’s cos the radiator isn’t hot enough)

[MrPotts]

2 hours ago, marshian said:

Do people not read posts

 

WC is turned off because it’s not working

 

when it is I may well ditch Wiser altogether 😉

Maybe WC wasn't working was because you were also using Wiser TRV's which were screwing up WC.

[JohnMo]

19 minutes ago, marshian said:

stops SWIMBO winding up the TRV’s

Or leave them as a placebo devise, just don't have them connected to anything functional.

[marshian]

24 minutes ago, MrPotts said:

Maybe WC wasn't working was because you were also using Wiser TRV's which were screwing up WC.

WC comp wouldn’t work with all the TRV heads removed 😉

 

It was heating water to weather comp 37 deg

 

Seriously it’s not a Wiser issue the boiler doesn’t know whats going on outside it’s flow and return temp and the volume of water passing thro it - sure TRV’s of any type (smart or dumb) can influence all of those things but so can balancing and pump speeds

 

There is no link between Wiser and the boiler other than a call for heat (either for HW or CH and currently the boiler doesn’t even know that as the HW demand box has been disabled as well as WC)

 

I’m sure it’ll get resolved fairly quickly because I’m not paying the bloody bill until it is 🙂

 

[marshian]

57 minutes ago, JohnMo said:

Or leave them as a placebo devise, just don't have them connected to anything functional.

I was intending if it all works as it should to just use the decorators caps - she turns those it turns the rad off